Ring oscillators are often used to provide clock signals having a controllable frequency. A ring oscillator typically consists of several series-connected delay stages, with the output of the last delay stage being fed into the first delay stage. The frequency of oscillation may be controlled by changing the delay associated with each delay stage. According to some techniques, this delay is changed by varying the resistance of a PMOS load located in each delay stage.
Some ring oscillator designs use interpolation to change the delay associated with each delay stage. According to one example, each delay stage provides two signal paths, with each path presenting a different delay. Control signals control an amount of interpolation between the delay of the slower path and the delay of the faster path. The resulting delay of the delay stage lies somewhere between the different delays presented by the two paths.